Everything You Need to Know About Diving with Manta Rays

Manta rays belong to the elasmobranch group, just like sharks. They have existed for around 5 million years, and they’re closely related to other rays you may find in the ocean. Their body is flattened, but they no longer live along the bottom of the sea. Instead, they move within the water column as if they are flying, elegantly using their modified, wing-like pectoral fins.

There are two species of manta: the Resident Reef Manta Ray and the Giant Oceanic Manta Ray. Both are plankton feeders, so instead of teeth, they use their gills in order to filter the microscopic food from the water. It’s thought that they can live between 40 and 50 years, but we still need more information to be able to establish their exact longevity.

Now let's see how to distinguish between the two species of manta ray.

Resident Reef Manta Ray

Mobula alfredi

Of the two species, the Reef Manta is the smallest, with an average disc-width of 10 to 11.5 feet (3-3.5 meters). The exception to this rule is the population of Mozambique, in which they can grow up to 13 to 15 feet (4-4.5 meters) wide. This species weighs around 2,900 pounds (1,300 kilos).

Females are larger than the males to accommodate their pup during “pregnancy.” The ventral part of the body is white with black spots, while the dorsal side is darker, forming a distinctive white or grey Y-shape along the ‘shoulders.’

As the name suggests, this species usually lives along coral reefs and makes short migrations according to the abundance of food.

The sting that is present in Stingrays is absent from all manta rays, so relax. Mantas are huge but not dangerous at all!

Photo credit: Jürgen Gangoly

Giant Oceanic Manta Ray

Mobula birostris

This manta ray can reach a considerable size, with an average width of 13 to 16.5 feet (4-5 meters) and sometimes up to 23 feet (7 meters). They can weigh up to 4,400 pounds (2,000 kilos)!

Its ventral part is white with black spots, but unlike the Resident Reef Manta, the pattern is not present in the area between the gills. Furthermore the lighter design on the dorsal side is T-shaped.

At the base of the giant manta’s tail is a fist-sized lump of cartilage. It’s an evolutionary remnant of the time they were sting rays (mantas evolved from sting rays). It’s nonfunctional.

Compared to the reef manta, this mysterious creature is harder to see because it tends to live in the open ocean and makes longer migrations. Consequently interactions with this animal are more difficult.

It’s worth mentioning that research regarding a third species of manta ray, tentatively referred to as the Atlantic or Caribbean Manta, is under way. This possible species has characteristics between the Oceanic and Reef Manta Rays. Genetic testing will likely confirm or reject this hypothesis in the near future.

Photo credit: Elias Levy

The "Black Morph" phenomenon

Both species of manta present three color morphs. The first morph is called “Chevron.” This is the classic manta color pattern. The dorsal part of the body is black with some white parts on the head and on the tips of the lateral fins. The belly is white with some black spots.

The second morph is astonishing. It is called “Black Morph.” The mantas presenting this particular morph are completely black dorsally and almost completely black ventrally, with white patches only near the gill areas.

The last color morph is “Leucism” or leucitic mantas. These mantas have less pigment than usual, and can look very white. They are not albino, as they still have some pigment (their eyes aren’t red). They might have some black on their tops, and very faded markings on their bellies. They are simply much much paler than a normally colored manta.

Photo credit: Tam Warner Minton

Manta or Mobula?

There are 9 species generally called Mobula. How do we distinguish them from manta rays? First of all they are usually smaller, with a maximum disc width of 10 feet (3 meters). Mantas and mobulas are both filter feeders, but mobula rays have a bottom jaw which is undercut, so that when their mouths are closed, the edge of the lower jaw rests much further back than the upper jaw. Manta rays’ jaws are aligned.

The cephalic fins of mobulas are also slightly different. When they are rolled up on themselves, they resemble horns. In fact, it is this feature that gives them the name devil rays.

The sting is absent in mobulas as well, except in the Spine-tail Devil Ray, where it is present but short.

Mobulas tend to travel in large groups. When found, divers usually enjoy swimming amongst hundreds of individuals at one time. However, mobulas are very shy and only approachable for a few moments.

Filter feeding machine

Manta rays feed primarily on plankton. Do you know what that is? Plankton is “the aggregate of passively floating, drifting, or somewhat motile organisms occurring in a body of water.” We can divide it into two groups: phytoplankton, made of microscopic plants and algae, and zooplankton, made mostly of microscopic animals.

Manta rays filter plankton through their modified gills, using their special cephalic fins as a funnel to increase the amount of food entering their mouth. Because they need to eat so much plankton, they have devised some fantastic feeding strategies:

Surface feeding: Manta rays swim at the surface of the water and feed by opening their mouth, swallowing large amounts of plankton. In these cases, it is easy to locate and observe them directly from the boat.

Somersaulting: One of the most beautiful spectacles that nature can offer. When there is a dense patch of plankton in the water column, some manta rays will do a backwards somersault in the water, circling around the plankton to optimize food intake. It is a wonderfully elegant show.

Bottom feeding: Individuals seem to scrape the bottom of the seabed. In reality they hover up to a few centimeters from the seabed where a lot of plankton is concentrated.

Forming feeding chains: When many manta rays are feeding in the same area and the concentration of plankton is high, they can form a “single file line.” In this way, the zooplankton which is missed by the first manta will be scooped up by the individual behind it. By cooperating with each other, mantas can increase the amount of food ingested.

Cyclone feeding: An incredible sight and a rare phenomenon, which can, for example, be seen a few times a year in the Maldives. When concentrations of plankton are extremely high, more than 30 manta rays create one huge feeding chain. Up to 200 manta rays can be seen in this formation. They start swimming in a spiral, creating a vortex. This pulls the plankton into the open mouths of the waiting mantas!

Photo credit: Niv Froman

Courtship and Reproduction

Being able to witness the courtship and reproduction of mantas in nature is a rare sight. Courtship usually starts at a cleaning station. When the female comes into estrus, she releases hormones that attract males.

Males usually follow the female for 20 minutes up to 48 hours, as she ‘tests’ the males’ strength and stamina by leading them on a “dance,” looping, swerving, and diving incredibly fast until there is only one male left. This male will take hold of the female’s left “wing” in his mouth, then move underneath the female so they are facing each other. Finally, copulation begins and takes just a few seconds.

Thanks to the marks left by the bite, it can be established if a female has already mated. After about a year, the female gives birth to one pup (rarely two). The pups are about 5 feet (1.5 meters) in width, and swim off without any nursing from the females. Unfortunately, it’s estimated that manta rays breed only every 3-5 years, resulting in a serious risk of extinction.

The number of pups who are born and survive is far lower than the number of manta rays killed by man.

Feeding Stations

These are areas where, during a certain period of the year, there is a greater concentration of food. These areas are usually seasonal places, because zooplankton follow the currents influenced by weather patterns (e.g. the monsoons in the Maldives).

Photo credit: Niv Froman

Cleaning Stations

Comparable to car washes! These are where manta rays come to have cleaner wrasse and other fish bite off all their dead skin, parasites and food detritus. It was observed that females, on average, spend more time in this kind of beauty center… a coincidence? ;)

Please look and do not touch. Avoid disturbing them and reduce interaction times.

Always try to use common sense and bring respect for these wonderful creatures.

Did you know…?

Origin of the Name

The origin of their nameis related to a legend. It says that centuries ago Spanish fishermen were frightened by a huge fish whose aspect resembled a large cloak (manta in Spanish). They feared that if they fell into the sea, the creature would wrap them up and drown them.

Never Stopping

If mantas stop swimming, they will sink! Mantas, like sharks, have a cartilaginous skeleton that is very light, saving them valuable energy. However, they still weigh more than a ton. They can control their buoyancy with the variation of an oily substance located in the liver and by simply swimming.

Reproduction is the Driving Force of Existence

Mother Nature gave two penises or claspers to male mantas. (What are claspers? And why do they have two? Click here for the answer).

You might think that if males have two penises, females have two vaginas. But this isn’t true. Females have only one vagina called a “cloaca,” an internal room where the reproductive, digestive and urinary ducts excrete their products.

Can Mantas Sting?

Mantas have no barbs. Rarely some individuals can show a useless barb on the posterior part of the dorsal fin. They are absolutely harmless. In fact, snorkeling and diving with them creates a close connection. However, it is always important to use good conduct while in the water with mantas. See the section “Code of Conducts.”

Brainy Mantas

Anatomical studies have shown that the manta brain is very large. In fact, it has the biggest brain to body ratio among the studied fish. It is thought that they have highly developed cognitive abilities and interesting studies are in progress. Do you remember the Whale Shark? The size of a whale shark can be ten times the size of a manta, but their brain is only a third of the size of a manta brain.

Most divers that have seen mantas note their strange behaviour. It seems that they are curious, and they tend to swim close to observe divers.

Jumping Mobulas

No one knows yet exactly why mobulas jump out of the water. Researchers think this behavior is a spectacular courtship ritual. Similar to humpback whales, it is thought that the jump is used to attract other individuals or display dominance through the noise produced. Jumping may also be a method for eliminating parasites or escaping from predators. Even mantas can do it, but it is much more rare to observe a jumping manta.

Threats and Solutions

The natural predators of manta rays are a few types of sharks, killer whales and false killer whales. Occasionally you may see a manta with the characteristic ‘half-moon’ shark bite on it’s wing. But the real danger to these sea creatures is, as always, humans and their activities. Hooks and fishing nets wound and trap mantas, often leading to death (bycatching).

The flavor and texture of their meat is not highly sought-after. However, their gills are. In Chinese traditional medicine, it is believed that their gills have medicinal properties, such as improving the immune system, preventing cancer and aiding nursing mothers. Without criticizing this holistic medicine, there is no scientific evidence supporting these uses and recent studies have shown manta rays possess toxic levels of heavy metals harmful to humans. (More that 20 times the WHO recommendation of safe arsenic level has been found in manta gill rakers.) The manta fishing industry is highly developed in countries such as Sri Lanka and India.

How can we stop this? Through awareness campaigns, sustainable fishing strategies, manta conservation projects that work to introduce sustainable alternatives and by avoiding products that use parts of mantas. But above all, you can travel and enjoy manta rays in their natural habitat. This will give a commercial value to them (ecotourism). In such a way, it will be more advantageous to keep mantas alive rather than to kill them.

Manta saviours

In the past few decades, the effort to study and protect mantas has increased. People, driven by their passion for the ocean, have created several associations. They have unified these energies to create networks with the purpose of the conservation of these wonderful creatures.

Credits

This article was written by Mario Passoni and Luca Saponari - two marine biologists involved in several projects concerning ocean conservation and education. Special thanks to Niv Froman, Tam Sawers, Sarah Lewis and Nicola Bassett from Manta Trust, Asia Armstrong from Project Manta and Anna Flam from the Marine Megafauna Foundation.